1. Field of the Invention
The present invention relates to a dye compound and, more particularly, to a dye compound which is used for the dye-sensitized solar cell (DSSC).
2. Description of Related Art
With the development of industrial technology, the serious problems the whole world is facing today are the energy crisis and the environmental pollution. In order to solve the global energy crisis and to reduce the environmental pollution, one of the effective means is the solar cell, which can convert the solar energy into the electricity. Since the dye-sensitized solar cell has the advantages of low manufacturing cost, large-scale production, great flexibility, light transmittance, and being capable of use in the buildings, the application of the dye-sensitized solar cell becomes more and more attractive.
Currently, Grätzel et al. have disclosed a series of literatures, for example, O'Regan, B.; Grätzel, M. Nature 1991, 353, 737, which show the practicability of the dye-sensitized solar cell. The general structure of the dye-sensitized solar cell comprises an anode, a cathode, a nano-porous titanium dioxide layer, a dye, and electrolyte, wherein the dye plays a critical role in the conversion efficiency of the dye-sensitized solar cell. The dye suitable for the dye-sensitized solar cell must have characteristics in broad absorption spectrum, high molar absorption coefficient, thermal stability, and light stability.
Grätzel's lab has published a serious of ruthenium complexes as the dyes for the dye-sensitized solar cell. Grätzel's lab published a dye-sensitized solar cell prepared with a N3 dye in 1993, and the conversion efficiency of the dye-sensitized solar cell is 10.0% under the illumination of AM 1.5 stimulated light. The incident photon-to-current conversion efficiency (IPCE) value of the N3 dye is 80% in the range of 400 to 600 nm. Although hundreds of dye complexes have developed, the conversion efficiency of those dye complexes is not as good as the N3 dye. The structure of the N3 dye is represented by the following formula (a).

In 2003, Grätzel's lab published a dye-sensitized solar cell prepared with a N719 dye, and the conversion efficiency of the dye-sensitized solar cell is improved to 10.85% under the illumination of AM 1.5 stimulated light, wherein the structure of the N719 dye is represented by the following formula (b).

Grätzel's lab also published a dye-sensitized solar cell prepared with a black dye in 2004, and the conversion efficiency of the dye-sensitized solar cell is 11.04% under the illumination of AM 1.5 stimulated light. The black dye can enhance the spectral response in red and near-IR region, so the conversion efficiency of the dye-sensitized solar cell can be improved. The structure of the black dye is represented by the following formula (c).

In addition to the ruthenium complexes such as the N3 dye, the N719 dye, and the black dye, other types of dye compounds, which can be used in the dye-sensitized solar cell, are platinum complexes, osmium complexes, iron complexes, and copper complexes. However, the results of various researches show that the conversion efficiency of the ruthenium complexes is still better than other types of dye compounds.
The ruthenium complexes are the sensitizer dyes with the highest conversion efficiency nowadays. However, the manufacturing cost of the ruthenium complexes is high, and there may be problems of short supply when the ruthenium complexes are used widely. The organic sensitizers for the dye-sensitized solar cell have advantages of high molar absorption coefficient. Besides, it is possible to produce various organic sensitizers through molecular design. Hence, dye-sensitized solar cells with different colors can be manufactured to improve the application flexibility of the dye-sensitized solar cells. In addition, it is also possible to change the color of the dye-sensitized solar cell to match with the color of objects. Currently, dye derivatives, such as coumarin (Hara, K.; Sayama, K.; Arakawa, H.; Ohga, Y.; Shinpo, A.; Sug, S. Chem. Commun., 2001, 569), indoline (Horiuchi, T.; Miura, H.; Sumioka, K.; Uchida, S. J. Am. Chem. Soc., 2004, 126 (39), 12218), and merocyanine (Otaka, H.; Kira, M.; Yano, K.; Ito, S.; Mitekura, H.; Kawata, T.; Matsui, F. J. Photochem. Photobiol. A: Chem.; 2004, 164, 67), have already applied in the manufacture of dye-sensitized solar cells.
The dyes for the dye-sensitized solar cell influence the conversion efficiency greatly. Hence, it is desirable to provide a dye compound, which can improve the conversion efficiency of the dye-sensitized solar cell.